Jacob Palaeologus, born Giacomo Massilara (Chios, c. 1520 – Rome, March 22, 1585) was a former Dominican monk who became an anti-Trinitarian.
He was born in Chios, Greece. The name Palaeologus is usually an indication of relation to the Byzantine Palaiologos nobility, though there is no indication that Giacoma della Massilara had such a relation.
Palaeologus came to Transylvania then Poland in 1575, where he was active among the (Socinian) Polish Brethren. However Fausto Sozzini and the Ecclesia Minor did not welcome Palaeologus' advocacy of Christian service in the military - such was acceptable in the Calvinist Ecclesia Major, but abstention from secular politics, whether by choice or by imposition, had become one of the marks of the Polish Brethren community.[1][2]
Palaeologus was apprehended in Moravia, and was sent by Rudolph II to Rome in 1582. On February 19, 1583, he was taken to the stake but abjured at the sight of the Portuguese Marani being burnt alive, and was permitted to return to his cell. The College of Cardinals argued for his death, but Pope Gregory XIII insisted that Palaeologus, if he would cooperate, would be more useful alive. However Palaeologus failed to cooperate, and was beheaded in 1585.[3]